Fast battery charger for a device having a varying electrical load during recharging

ABSTRACT

In an exemplary fast charging system, a hand-held computerized terminal with rechargeable batteries therein may be bodily inserted into a charger receptacle. The terminal may have volatile memory and other components requiring load current during charging. The system may automatically identify battery type and progressively increase charging current while monitoring for an increase in battery terminal voltage to ascertain the level of load current. The battery temperature may be brought into a relationship to surrounding temperature such that by applying a suitable overcharge current value and observing any resultant temperature increase, the level of remaining battery charge can be determined. For example, if the battery is found to be relatively fully discharged, a relatively high fast-charge rate may be safely applied while monitoring battery temperature. If the battery is initially relatively fully charged or reaches such a state during fast charge, the system may automatically switch to a lower sustainable overcharge rate selected according to battery type and temperature. A preferred system any automatically recharge the battery of a portable device according to an optimum schedule of essentially maximum safe charging rates as a function of battery temperature. The system may also convert a regulated charging current to a pulsed and modulated waveform to provide efficient net charging to the battery. The source of charging current can optionally be placed outside the terminal housing to eliminate any heat dissipation effects of the current source.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 07/837,650filed Feb. 18, 1992, now U.S. Pat. No. 5,463,305 which in turn is acontinuation-in-part of applications Ser. No. 07/769,337 filed Oct. 1,1991, now U.S. Pat. No. 5,278,487, Ser. No. 07/478,180 filed Feb. 9,1990, now abandoned, and Ser. No. 07/446,231 filed Dec. 5, 1989, nowabandoned.

Said application Ser. No. 07/769,337 is a continuation-in-part ofapplications Ser. No. 07/544,230 filed Jun. 26, 1990, now abandoned,Ser. No. 07/478,180 filed Feb. 9, 1990, now abandoned, and Ser. No.07/446,231 filed Dec. 5, 1989, now abandoned.

Said Ser. No. 07/544,230 is a continuation-in-part of applications Ser.No. 07/478,180 filed Feb. 9, 1990, now abandoned, Ser. No. 07/446,231filed Dec. 5, 1989, now abandoned, Ser. No. 07/422,226 filed Oct. 16,1989, now U.S. Pat. No. 4,961,043, and Ser. No. 07/266,537 filed Nov. 2,1988, now abandoned.

Said Ser. No. 07/478,180 filed Feb. 9, 1990 is a continuation-in-part ofapplications Ser. No. 07/446,231 filed Dec. 5, 1989, now abandoned, Ser.No. 07/422,226 filed Oct. 16, 1989, now U.S. Pat. No. 4,961,043, andSer. No. 07/266,537 filed Nov. 2, 1988, now abandoned.

Said Ser. No. 07/446,231 filed Dec. 5, 1989 is a continuation-in-part ofapplications Ser. No. 07/422,226 filed Oct. 16, 1989, now U.S. Pat. No.4,961,043, Ser. No. 07/266,537 filed Nov. 2, 1988, now abandoned, andSer. No. 07/168,352 filed Mar. 15, 1988, now U.S. Pat. No. 4,885,523.

Said Ser. No. 07/422,226 filed Oct. 16, 1989 is a continuation-in-partof applications Ser. No. 07/266,537 filed Nov. 2, 1988, now abandoned,and Ser. No. 07/168,352 filed Mar. 15, 1988, now U.S. Pat. No.4,885,523.

Said Ser. No. 07/266,537 filed Nov. 2, 1988 is a divisional of Ser. No.07/168,352 filed Mar. 15, 1988, now U.S. Pat. No. 4,885,523, which is acontinuation-in-part of Ser. No. 06/944,503 filed Dec. 18, 1986, nowU.S. Pat. No. 4,737,702 which is a continuation-in-part of applicationsSer. No. 876,194 filed Jun. 19, 1986, now U.S. Pat. No. 4,709,202, andU.S. Ser. No. 797,235 filed Nov. 12, 1985, now U.S. Pat. No. 4,716,354.

Said Ser. No. 876,194 is a division of U.S. Ser. No. 797,235 filed Nov.12, 1985, now U.S. Pat. No. 4,716,354, which is a continuation-in-partof application Ser. No. 612,588 filed May 21, 1984, now U.S. Pat. No.4,553,081, which is a continuation-in-part of Ser. No. 385,830 filedJun. 7, 1982, now U.S. Pat. No. 4,455,523.

INCORPORATION BY REFERENCE

The disclosures and drawings of the above-mentioned U.S. Pat. Nos.4,455,523, 4,553,081, 4,737,702, 4,885,523 and of the pendingapplications U.S. Ser. No. 07/266,537, U.S. Ser. No. 07/446,231, andU.S. Ser. No. 07/478,180 are hereby incorporated herein by reference intheir entirety.

BACKGROUND OF THE INVENTION

NiCad (nickel-cadmium) battery technology has been employed successfullyin portable hand-held applications for many years. Photographicequipment, power tools, data terminals, personal radio transceivers, andpagers commonly utilize NiCad batteries as a power source. The chargingsystems that have been provided with these products have ranged from asimple transformer/rectifier type to rather complex systems to monitorand control the charging function. An increasing need is the ability tocharge NiCad batteries quickly. To reliably and efficiently charge NiCadbatteries at high rates requires careful control of the chargingoperation to avoid damage to the cells, particularly under extremeambient temperature conditions.

The NiCad charge cycle consists of two basic parts: the coulombicportion and the overcharge portion. The coulombic portion of the chargecycle is characterized by the fact that most of the charge that isapplied to the battery is stored in the form of electrochemical energy.This portion of the charge cycle is slightly endothermic, consequentlyhigh charge currents may be applied during this time without resultingin temperature increase. Most of the available battery capacity isstored during the coulombic portion of the charge cycle. The overchargeportion of the charge cycle is characterized by the fact that most ofthe applied charge current causes generation of oxygen gas at thepositive electrode of the NiCad cell, with only a relatively smallamount of charge actually being stored in the cell. The released oxygenchemically recombines with cadmium at the negative electrode of the cellwhich serves to equalize the internal pressure of the cell. If theovercharge rate is too high, the rate of oxygen recombination may beinsufficient to prevent excessive internal pressure and cell venting,which drastically reduces the useful life of the cell.

The most critical factors in determining the maximum allowable chargecurrent that may be safely applied to a NiCad battery are temperatureana state of charge. At low temperatures the oxygen recombination rateis significantly reduced which limits the allowable overcharge currentthat may be applied without venting the cells if they are fully charged.At high temperatures the heat released by the oxygen recombinationreaction may cause excessive cell temperature to be experienced leadingto premature failure of the plate separator material and subsequentshort-circuiting.

If the battery is fully discharged, minimal oxygen generation will occuruntil the battery nears the fully charged condition. If the battery isnearly fully charged, it will quickly enter the overcharge condition andbegin oxygen generation. The difficulty lies in accurate determinationof the previous state of charge to avoid damage to the battery.

Additionally, battery chargers sometimes use a constant-current sourceto charge batteries. If a varying load is placed in parallel with abattery under charge, the current delivered to the battery may not besufficient to charge it in a specified time. If the load is too great,the battery may actually be discharged. This is particularly true if theconstant current source producing the charging current does not have thecapability of adequately servicing both battery recharging and varyingload, or with a varying load is too unpredictable in magnitude orduration to insure it will not adversely affect battery recharging.

One solution to this problem is to provide a current source which iseither variable or without question can produce enough current to handleall situations regarding battery charging and varying load. However, asignificant problem with these types of current source is thepossibility of excessive heat dissipation which can adversely affecteither the recharging process, operation of the device, or both.

Still further, there is room for improvement in recharging batteries ofthe type being discussed. A variety of factors can interfere with theeffective and efficient charging of batteries. An improvement in theflexibility and efficiency of recharging would be desirable in the art.

SUMMARY OF THE INVENTION

A basic objective of the present invention is to provide a monitoringand control system which provides for effective fast charging. In orderto avoid damage to the battery, the system automatically tests todetermine the initial state of charge and selects the charging rateaccordingly.

In a preferred implementation, a microprocessor receives measures ofbattery temperature and battery terminal voltage and selects an optimumcharging rate. A unique feature of the preferred system is its abilityto provide a safe controlled charge to a NiCad battery without sensingthe current flow through the battery directly. This allows the effectivebattery impedance to be held at a minimum, thereby delivering themaximum available battery energy to the load.

Further features of the preferred system relate to the automaticprocessing of batteries subject to temperature extremes beyond the rangewhere rapid charging operation is permitted.

An additional objective or feature of the invention is to accommodate avarying load and effective charging of the batteries while connected toa constant current charging source. A further feature is the ability toremove circuitry from the body of the device holding the batteries whichmay generate heat which is detrimental to the device or batteries.

A still further feature of the present invention relates to a flexibleyet very efficient way to recharge batteries so that effectiverecharging can be accomplished regardless of the nature of theenvironment, the load on the device, or other factors involved with thedevice or the charging current source.

The invention will now be described, by way of example and not by way oflimitation, with references to the accompanying sheets of drawings; andother objects, features and advantages of the invention will be apparentfrom this detailed disclosure and from the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-17 and the brief description thereof are incorporated herein byreference to U.S. Ser. No. 876,194, now U.S. Pat. No. 4,709,202 issuedNov. 24, 1987.

FIG. 18 is an electric circuit diagram for illustrating a preferredembodiment of battery charging current control system in accordance withthe present invention;

FIG. 19 shows an exemplary current pulse waveform which may correspondwith a maximum battery charging rate in a substantially linear operatingrange for an exemplary control system in accordance with FIG. 18;

FIG. 20A shows selected control pulses which may be generated duringcontrol of battery charging current in the control system of FIG. 18,and FIG. 20B shows respective corresponding battery charging currentpulses on the same time scale with vertically aligned portions of thewaveforms of FIGS. 20A and 20B occurring at the same time;

FIG. 21 is a diagrammatic view of use in explaining the aliased samplingof actual current pulses in the battery charging circuit, andillustrating the case where thirty-two samples form a complete samplingcycle;

FIG. 22 is a block diagram for illustrating exemplary sampling circuitryfor association with the V sense input of the processor means of FIG.18;

FIG. 23 illustrates a battery conditioning system as described at col.17, lines 51-68 of the incorporated U.S. Pat. No. 4,455,523, and whereintwo-way communication may be established between memory means associatedwith a portable unit comprised of rechargeable battery means, andnon-portable central computer controlled conditioning station;

FIG. 24 shows a battery conditioning system wherein a batteryidentifying circuit element directly controls the set point of a batterycharging circuit to determine a battery charging parameter, e.g.,battery charging current;

FIG. 25 shows a highly integrated semiconductor device, e.g. forimplementing the system of FIGS. 18-22;

FIG. 26 is an electric circuit block diagram showing a batteryconditioning system wherein a preferred hand-held terminal unit containsbattery parameter sensing means and computer operating means foroptimizing battery charging current as supplied by an external circuit(which may correspond with a standardized circuit such as shown in FIG.24 applicable to a-complete family of hand-held terminals);

FIG. 27 shows a new RF terminal unit including charge control andtemperature transducer outputs as in FIG. 26, and also incorporating aninterface for coupling with a local area network so as to enable batchtransmission of data to and from the RF terminal;

FIG. 28 is a block diagram illustration of a preferred fast chargingsystem in accordance with the present disclosure;

FIG. 29 (sheets one and two) shows a flow chart for illustrating apreferred fast charging algorithm for use with the microprocessor ofFIG. 28;

FIG. 30 is a circuit diagram illustrating a preferred arrangement forthe automatic identification of various types of batteries which may beassociated with a fast charging system according to FIGS. 28 and 29;

FIG. 31 is a diagram useful in explaining certain steps of the flowchart of FIG. 29;

FIG. 32 is a circuit diagram for illustrating an exemplaryimplementation of the block diagram of FIG. 28;

FIG. 33 illustrates a plot showing a maximum permissible overcharge ratefor fast charge cells as a function of cell temperature, and providesinformation which may be incorporated in the programming of the systemof FIGS. 28-32 for establishing an optimum value of charging current(Ichg) during sustained overcharging;

FIG. 34 illustrates a plot of maximum charge rate for first charge cellsas a function of cell temperature to show exemplary data which may beused for the system programming in FIGS. 28-32 for establishing anoptimum value of charging current for a battery which has not yetreached the overcharge state;

FIG. 35 shows a plot of measured battery pack temperature as a functionof time for a previously fully charged enclosed battery pack where anovercharge current (Ichg) of three hundred milliamperes is applied andthe ambient temperature T_(A) is about fourteen degrees celsius (14° C.)and also illustrates successive approximate slope values for selectedsuccessive time intervals; and

FIG. 36 is a plot of measured battery pack temperature as a function oftime for the case of an enclosed battery pack which is initially at amuch lower temperature than ambient temperature; specifically thebattery pack was initially at a temperature of about minus fifteendegrees celsius (-15° C.) while the ambient temperature was about twentydegrees celsius (20°), the battery pack receiving only a small chargingcurrent of six milliamperes; FIG. 36 also shows successive approximateslope values by means of straight lines covering successive equal timeintervals of 600 seconds;

FIG. 37 shows an improved procedure for carrying out fast charging andmaintenance of a nickel-cadmium battery pack, for example in conjunctionwith a microprocessor system as shown in FIG. 28, the variable P temp, Vbatt and Atemp of FIG. 28 being represented by PT, PV and AT in FIG. 37;

FIG. 38 is a schematic diagram for illustrating a charge currentregulator circuit such as indicated at 28-20 in FIG. 28; and

FIG. 39 shows the voltage to current transfer function for the circuitof FIG. 38.

FIG. 40 is a block diagram of a closed loop battery charging circuit tocontrol the nature of the charging current to increase the efficiency ofcharging of the battery even under varying load.

FIG. 41 is an electrical schematic showing a charging current controlscheme for efficient battery recharging where the recharging currentsource is located externally of the housing of the battery andassociated device.

FIG. 42 is an electrical schematic similar to FIG. 41 showingspecifically a circuit combination utilizing a closed loop feed back fora controlled transistor switch to control charging current to thebattery.

FIG. 43 is a graph of a pulse width modulated signal illustrative ofwhat could be generated by the circuitry of FIG. 42.

FIG. 44 is an electrical schematic with alternative circuitry to that ofFIG. 42 for providing a pulse width modulated recharging current to thebattery but where the pulses are modified from a generally square waveto a generally trapezoidal wave.

FIG. 45 is a diagram of a trapezoidal-shaped current pulse illustrativeof what could be produced by the circuitry of FIG. 44.

FIG. 46 is a diagram of the voltage pulse generated in conformance withthe current pulse of FIG. 45.

DETAILED DESCRIPTION

The detailed description of FIGS. 1 through 27 is incorporated herein byreference to the specification at col. 4, line 25, through col. 66, line4, of the incorporated U.S. Pat. No. 4,709,202, by reference to thespecification at col. 4, line 15, through col. 11, line 37 of theincorporated U.S. Pat. No. 4,737,702, and by reference to thespecification of incorporated U.S. Pat. No. 4,885,523.

DESCRIPTION OF FIGS. 28-32

A block diagram of the charging system is shown in FIG. 28. Amicroprocessor 28-10 is preferably of a type that has analog to digitalinputs such as 28-11 to 28-13 and digital to analog outputs such as28-14 for interface to sensor and control. functions. Both thetemperature of battery 28-15 and ambient temperature are sensed asindicated at 28-16 and 28-17 so that absolute and relative temperaturemeasurements may be made. The terminal voltage of the battery pack issensed as indicated at 28-12 so that charge trends may be determined.The charge regulator consists of a voltage controlled current source28-20 whose output current (Ichg) is controlled by the level of thecharge control signal at 28-14 from the microprocessor. A load 28-21 mayor may not be connected during charge.

In the microprocessor 28-10, analog to digital (A/D) means and digitalto analog (D/A) means are indicated at 28-10A and 28-10B. Preferablythese means are integrated with the other components of themicroprocessor as part of a monolithic unit or "chip" formed from aunitary substrate of semiconductor material.

With a charging system as shown in FIG. 28, an algorithm has beendeveloped for fast charging of NiCad batteries as shown in FIG. 29(sheets one and two). The charging function is initiated as representedby "start" at 29-1 e.g. by placing the battery 28-15 in the charger. Thetemperature sensor 28-16 is preferably in a housing 28-22 which togetherwith battery 28-15 forms the battery pack 28-25. The sensor 28-16 ispreferably of the type whose output is proportional to absolutetemperature e.g. at the rate of ten millivolts per degree Kelvin (10mv/° K). The microprocessor 28-10 tests for insertion of the battery inthe charger by reading the temperature Ptemp as indicated at 29-2, andchecking to determine if Ptemp shows a temperature greater than -1000°C.; see decision block 29-3. The decision at block 29-3 will beaffirmative only if a battery pack has been inserted to provide anon-zero voltage on the Ptemp signal line 28-11.

Following determination of the presence of a battery pack 28-25 in thecharger, the pack type must be identified as represented at 29-4 and29-5 to allow for cells with different charge characteristics. In thecase of an invalid reading of battery pack identity, the program maybranch to an error sub routine as indicated at 29-5A. The identificationof the type of battery inserted into the charger is a significant stepin the battery processing operation since battery cells of specializedtypes may offer significantly higher capacity than ordinary NiCad cells,but they may require charging at lower maximum rates. Other cells mayallow high charging rates at extreme temperatures. Future technologydevelopments may offer new cell types with unusual charging parametersthat may be accommodated by applying an appropriate charging algorithm.As shown in FIG. 30, a proposed method for identification of the packtype is to connect a shunt voltage regulator 30-10 to the battery pack30-27 represented in FIG. 30. The shunt regulator may consist of asimple zener diode or it may be implemented with an active regulatore.g. as indicated in FIG. 30, depending on the number of different packtypes that must be identified. Upon determination of the pack type asuitable one of a set of parameter tables may be selected that containsthe appropriate values for charging the specified cell type, as shown at29-6.

As indicated in FIG. 28, there may be a load 28-21 placed on the batterythat requires current. Consequently, current supplied by a charger isshared by the load and the battery as shown in FIG. 31. If the loadcurrent Iload is larger than the charge current Ichg, the battery willprovide the difference, resulting in further discharge of the batteryrather than charging. To compensate for this effect, the algorithmsenses the terminal voltage (Vb) of the battery (step 29-7, FIG. 29) andapplies increasing charge current to the battery in small increments(step 29-8) until the terminal voltage trend is positive (steps 29-9 to29-11) meaning the battery is accepting charge rather than providingcurrent to a load (see block 29-12).

While the absolute terminal voltage of a NiCad battery is a poorindicator of its condition, its trend is a good indicator of chargingversus discharging if it is measured over a short enough time that thepack temperature remains relatively constant. Once the battery voltagetrend is determined to be positive, the level of current required by theload (Iterm of block 29-12 corresponding to Iload, FIG. 31) is known,and may be added to the desired net battery current level (Ibatt, FIG.31) to select the actual charge current (Ichg, FIG. 31).

Typical NiCad cell specifications call for charging in a temperaturerange of 0° to 40° C. Many of the products that utilize NiCad batteriesmay operate in environments with temperatures that range from -30° C. to60° C. Consequently, it is possible that a battery pack may be placed ina charger immediately after being removed from either of thesetemperature extremes. If the pack temperature is greater than 40° C.,(see decision step 29-13), the pack must be "cooled" to no more than 40°C. before charging may proceed. This is accomplished (as shown by step29-14) by applying a charge current Ichg that equals the terminal loadIterm so that no net charge current is received by the battery and itmay be cooled by the ambient environment. If the battery pack is cold,it must be warmed to a temperature above 0° C. This is carried out bysteps 29-15 to 29-19. By applying a safe (low) charge current per thecharge table of steps 29-17 and 29-19 (and FIG. 33), the pack my bewarmed by the ambient environment of the charger.

Although charging may begin when the battery temperature exceeds 0° C.according to the battery charging specifications, additional informationis needed to determine the state of charge of the battery. The clearestmethod to determine whether a battery is fully charged is to detect thepresence of the overcharge condition. In overcharge, the oxygenrecombination reaction is highly exothermic which results in rapidheating of the battery. By applying twice the permissible substainedovercharge rate as at steps 29-20 to 29-23 and monitoring celltemperature, it is possible to reliably determine that the overchargecondition has been reached. Unfortunately, when a cold pack is placed ina warm environment, there is a resultant temperature rise due to ambientwarming that can actually occur at a rate faster than the heating due tothe supply of a high value of overcharge current. Consequently, the onlyreliable means of detecting heating due to overcharge current is firstinsure that the battery temperature is not substantially less than theambient temperature (as determined by step 29-18). Once the battery iswarmed to ambient temperature, the overcharge condition can be quicklydetected by means of steps 29-20 to 29-23 since any further substantialincrease in temperature can be attributed to internal heat being evolvedby the battery. If the pack has been in a hot environment, the cooling(steps 29-13 and 29-14) will bring its temperature down to no more than40° C., which is above the ambient temperature of the charger.Overcharge induced heating will cause the pack temperature to begin toincrease again as shown by FIG. 35. According to the describedalgorithm, the charge current applied to the battery for overchargedetection (step 29-20) is double the standard overcharge table value ofsteps 29-17, 29-19 and 29-28 (and of FIG. 33) to improve the ability todetect a temperature increase. Since the test time is relatively short,little gas pressure increase and potential for cell venting is involved.

Once it has been determined that the battery is not In the overchargecondition (at decision block 29-23), it is a relatively simple matter toapply the appropriate charge value from the fast charge parameter table(as at step 29-24, FIG. 29). The fast charge table value may correspondto that indicated in FIG. 34 and is a function of temperature so that atemperature regulation capability is implemented for reducing thecurrent applied at elevated temperatures. During the fast chargeoperation, battery temperature increase is closely monitored (steps29-25 to 29-27) to determine when overcharge has been reached, so thatthe fast charge cycle may be terminated (as represented by branch line29-27a) and a controlled temperature overcharge cycle may be initiatedas represented by step 29-28 and FIG. 33 to "top-off" the battery formaximum capacity. After the overcharge cycle is complete (after step29-29), a trickle charge current is applied per step 29-30 to maintainthe full battery capacity and offset the effects of self-dischargenormally seen when a battery rests in an idle condition.

FIG. 32 shows a preferred embodiment of the described fast chargingsystem utilizing a microprocessor system with a programmed algorithm forfast charging of battery packs. Other embodiments involving controlcircuits contained within a data terminal or other utilization devicemay employ identical algorithms without departing from the conceptsdescribed.

FIG. 32 represents an implementation of FIG. 28, and correspondingreference numerals have been applied in FIG. 32 so as to facilitatecorrelation therewith. The major components of. FIG. 32 may comprisecommercially available parts which are identified as follows:

microprocessor chip 32-10 of microprocessor system 28-10, type SC83C552

voltage regulator 32-11, type LP2951AC

amplifiers 28-12 and 28-13 of charge regulator 28-20, type LT1013transistor 32, type 1RF9Z30

temperature sensor 28-17,type LM335

The programming for microprocessor element 32-10 of FIG. 32 maycorrespond with that represented in FIGS. 29, 33 and 34, as describedwith reference to these figures and the circuits of FIGS. 28, 30 and 31.By way of example, terminals 32-21, 32-22, 32-23 and 32-24, FIG. 32, maybe connected with terminals 30-21, 30-22, 30-23 and 30-24 respectivelyin FIG. 30. Temperature sensor 30-26, FIG. 30, which is connectedbetween terminals 30 and 30-23, may correspond with sensor 28-16 and maybe mounted in intimate heat transfer relation with battery 28-15 andwithin the housing of the battery pack 28-25 as represented in FIG. 28.Resistor R1, FIG. 30, has a respective one of a set of values so as toprovide a voltage level between terminals 30-22 and 30-24 selected so asto identify the particular type of battery pack 30-27 with which it isassociated.

Terminals 30-21A, 30-22A, 30-23A and 30-24A may be connected with autilization circuit to supply energy thereto during portable operation.It will be noted that the battery pack 30-27 can be associated with thecircuitry of FIGS. 16A and 16B hereof (corresponding to FIGS. 16A and16B of incorporated U.S. Pat. No. 4,709,202), terminals 30-21A and30-22A having a quick-release connection with terminals JP-1, JP-2, FIG.168, and terminals 30-23A having a quick-release coupling with terminalJ7-3, FIG. 16B. Terminal 30-24A can be used by the portable device toidentify the battery pack, where the portable device provides a circuitsuch as associated with terminal 32-24, FIG. 32, leading to an analog todigital input such as 32-25, FIG. 32.

FIG. 35 illustrates by a plot 35-10 the increase in temperature as afunction of time of an enclosed battery pack such as 27-10B, FIG. 27,28-25, FIG. 28 or 30-27, FIG. 30, due to an overcharge current of 300milliamperes, where the battery means 27-27, 28-15 is initially fullycharged and is at a battery temperature of about minus eight degreescelsius, the ambient temperature being about fourteen degrees celsius.The slopes between successive points 35-1, 35-2, 35-3 and 35-4, arerepresented by straight line segments 35-11, 35-12 and 35-13, withrespective slope values of 0.54 degrees celsius per minute, 0.36 degreescelsius per minute and 0.21 degrees celsius per minute.

FIG. 36 for the sake of comparison shows by a curve 36-10 the rate ofwarming of such a battery pack due to an ambient temperature which issubstantially higher than battery temperature. Specifically FIG. 36shows the case where initial battery temperature is about minus fifteendegrees celsius and ambient temperature is about twenty degrees celsius.Straight line segments 36-11, 36-12, 36-13, 36-14 show approximate slopevalues of 0.98 degrees celsius per minute, 0.5 degrees celsius perminute, 0.33 degrees celsius per minute and 0.24 degrees celsius perminute. The relatively high slope values indicate that the differentialbetween a high ambient temperature and a low battery temperature must betaken into account when using steps 29-20 to 29-23 to determine whethera battery is in the overcharge range.

DISCUSSION OF FIGS. 33 THROUGH 36 AND TABLES I AND II

FIGS. 33 and 34 represent in effect a series of tables of charge rateversus temperature since the ordinate values are in units of charge rate(e.g. current Ibatt in milliamperes divided by capacity C inmilliampere-hours). The following TABLES I and II give values ofovercharging and fast charge corresponding to FIGS. 33 and 34 forsuccessive temperatures in increments of degrees celsius, and givecorresponding current values in milliamperes for two different values ofbattery capacity C, namely C equals 800 milliampere-hours and C equals1200 milliampere hours.

                  TABLE I                                                         ______________________________________                                        Charge Table: Overcharge and Fast Charge                                      Battery type: 800 ma-hr fast charge                                                   Overcharge value  Fast Charge value                                   Temp, °C.                                                                        C. units                                                                              ma.         C. units                                                                            ma.                                       ______________________________________                                        -30       0.040    32         0.160 128                                       -28       0.044    35         0.176 141                                       -26       0.048    38         0.192 154                                       -24       0.052    42         0.208 166                                       -22       0.056    45         0.224 179                                       -20       0.060    48         0.240 192                                       -18       0.068    54         0.264 211                                       -16       0.076    61         0.288 230                                       -14       0.084    67         0.312 250                                       -12       0.092    74         0.336 269                                       -10       0.100    80         0.360 288                                       -8        0.120    96         0.408 326                                       -6        0.140   112         0.456 365                                       -4        0.160   128         0..504                                                                              403                                       -2        0.180   144         0.552 442                                        0        0.200   160         0.600 480                                        2        0.220   176         0.742 594                                        4        0.240   192         0.886 709                                        6        0.260   208         1.029 823                                        8        0.280   224         1.171 937                                       10        0.300   240         1.314 1051                                      12        0.300   240         1.457 1166                                      14        0.300   240         1.600 1280                                      16        0.300   240         1.600 1280                                      18        0.300   240         1.600 1280                                      20        0.300   240         1.600 1280                                      22        0.300   240         1.600 1280                                      24        0.300   240         1.600 1280                                      26        0.300   240         1.600 1280                                      28        0.300   240         1.600 1280                                      30        0.300   240         1.600 1280                                      32        0.300   240         1.600 1280                                      34        0.300   240         1.600 1280                                      36        0.300   240         1.340 1072                                      38        0.300   240         1.080 864                                       40        0.300   240         0.820 656                                       42        0.260   208         0.560 448                                       44        0.220   176         0.300 240                                       46        0.180   144         0.275 220                                       48        0.140   112         0.250 200                                       50        0.100    80         0.225 180                                       52        0.090    72         0.200 160                                       54        0.080    64         0.175 140                                       56        0.070    56         0.150 120                                       58        0.060    48         0.125 100                                       60        0.050    40         0.100  80                                       ______________________________________                                    

                  TABLE II                                                        ______________________________________                                        Charge Table: Overcharge and Fast Charge                                      Battery type: 800 ma-hr fast charge                                                   Overcharge value  Fast Charge value                                   Temp, °C.                                                                        C. units                                                                              ma.         C. units                                                                            ma.                                       ______________________________________                                        -30       0.040   48          0.160 192                                       -28       0.041    53         0.176 211                                       -26       0.048    58         0.192 230                                       -24       0.052    62         0.208 230                                       -22       0.056    67         0.224 269                                       -20       0.060    72         0.240 280                                       -16       0.066    82         0.264 317                                       -16       0.076    91         0.288 346                                       -14       0.084   101         0.312 374                                       -12       0.092   110         0.336 403                                       -10       0.100   120         0.360 432                                       -8        0.120   144         0.408 490                                       -6        0.140   168         0.456 547                                       -4        0.160   192         0.504 605                                       -2        0.180   216         0.552 662                                        0        0.200   240         0.600 720                                        2        0.220   264         0.742 890                                        4        0.240   286         0.866 1063                                       6        0.260   312         1.029 1280                                       8        0.280   336         1.171 1280*                                     10        0.300   360         1.314 1280*                                     12        0.300   360         1.457 1280*                                     14        0.300   360         1.600 1280*                                     16        0.300   360         1.600 1280*                                     18        0.300   360         1.600 1280*                                     20        0.306   360         1.600 1280*                                     22        0.300   360         1.600 1280*                                     24        0.306   360         1.600 1280*                                     26        0.300   360         1.600 1280*                                     28        0.300   360         1.600 1280*                                     30        0.300   360         1.600 1280*                                     32        0.300   360         1.600 1280*                                     34        0.300   360         1.600 1280*                                     36        0.300   360         1.340 1260*                                     38        0.300   360         1.080 1280*                                     40        0.300   360         0.820 984                                       42        0.260   312         0.560 672                                       44        0.220   264         0.300 360                                       46        0.180   216         0.275 330                                       46        0.140   168         0.250 300                                       50        0.100   120         0.225 270                                       52        0.090   108         0.200 240                                       54        0.080    96         0.175 210                                       56        0.070    84         0.150 180                                       58        0.060    72         0.125 150                                       60        0.050    60         0.100 120                                       ______________________________________                                         *note: maximum charge current available is 1280 ma.                      

TABLES I and II may be stored in machine readable form in the memory ofmicroprocessor system 28-10 or 32-10, e.g. in first and second read onlymemory segments. Thus if step 29-4 identified an 800 milliampere-hourcapacity fast charge nickel-cadmium battery means, the microprocessorwould access the first memory segment corresponding to TABLE I for stepssuch as 29-17, 29-19, 29-20, 29-24 and 29-28, while if step 29-4 showeda 1200 milliampere-hour capacity fast charge nickel-cadmium batterymeans the second memory segment corresponding to TABLE II would beaddressed.

If for example, the battery temperature (Ptemp) in step 29-16 weregreater than nineteen degrees celsius but less than or equal totwenty-one degrees celsius, the overcharge value read from memorysegment I would be 240 milliamperes (0.300 units in FIG. 33 times 800milliampere-hours, the battery capacity C, equals 240 milliamperes).Thus according to step 29-17 and step 29-19, an overcharge current of240 milliamperes (plus any needed load current) would be supplied byregulator 28-20 until temperature sensor 28-16 showed that batterytemperature exceeded ambient temperature (Atemp, 28-13, FIG. 28).

If ambient temperature were thirty degrees celsius and the batterytemperature were in the range from thirty-one to thirty-three degreescelsius, a current of 480 amperes would be applied according to step29-20, but for a limited duration (e.g. about ten minutes per step29-21) such as to avoid substantial detriment to the useful life of thebattery means.

FIG. 36 illustrates warming of the battery pack as a function of timewith the battery pack initially at a temperature of about minus fifteendegrees celsius. From FIG. 33, it can be seen that maximum permissibleovercharge current corresponds to about 0.08 units. For a batterycapacity of 800 milliampere hours, this would correspond to anovercharge current value of greater than sixty milliamperes, while FIG.36 shows the warming rate with an ambient temperature of about twentydegrees celsius and a relatively negligible value of charging current(i.e. Ichg equals six milliamperes). It will be noted that the warmingrate in FIG. 36 in the first 600 seconds is 0.98 degrees celsius perminute which considerably exceeds the warming rate produced by a currentof 300 milliamperes in FIG. 35.

Supplementary Discussion of FIGS. 28-36

For representing an embodiment such as that of FIG. 30, a microprocessorsystem such as indicated at 28-10 in FIG. 28 would be shown with afourth input to A/D means 28-10A corresponding with input 32-25, FIG.32. For such an embodiment each type of battery means such as the onewith 800 milliampere-hour capacity and temperature characteristics asshown in Table I, and the one with 1200 ampere-hour capacity andcharacteristics according to Table II would have a respective distinctvalue of and a respective different shunt voltage level so as to enablethe microprocessor system 28-10 to reliably identify each of numeroustypes of battery means pursuant to step 29-4. The microprocessor system28-10 or 32-10 may store a set of parameter tables such as Tables I andII in machine readable form with each table of such set having anaddress associated with the corresponding shunt voltage level. In thisway the appropriate stored table can be interrogated by themicroprocessor in accordance with a given battery temperature reading soas to obtain appropriate current values for steps 29-8, 29-17, 29-19,29-20, 29-24 and 29-28.

The battery identification means 26-36 or 30-10 would distinguish thepresence or absence of an internal current regulator 26-28 as well asidentifying the various battery types requiring different charging andovercharge treatment.

Other stored machine readable tables of computer system 28-10 or 32-10may include acceptable maximum overcharge rates as represented in FIG. 6and have charge rates, e.g., as described at Col. 9, line 26 to Col. 10,line 32 of the incorporated U.S. Pat. No. 4,455,523. Such stored tableswould insure that the charging system of FIG. 28 or FIG. 32 would becompatible with a battery means such as shown in FIG. 5 or in FIGS. 9Aand 9B. For example, the stored table for the battery means of FIGS. 9Aand 9B could take account of internal heating within the internalregulator 173 of .the battery pack and insure that the current thebattery (20, FIG. 5) and to the battery load did not exceed the powerdissipation capacity of the internal regulator network (173, FIG. 9A).

The current regulator 28-20 may be controlled to provide a voltage VCHGat the line CHG in FIG. 9A of approximately seven volts which wouldresult in minimum power dissipation in the interior regulator network(173, FIG. 9A). The presence of an internal current regulator within ahand-held terminal unit is indicated at 26-28, FIG. 26, and chargingcurrent control circuit 26-22 could conform with the embodiments ofFIGS. 28-36 in the selection of charging and overcharge current valueswhile tending toward minimum power dissipation in the internal regulatornetwork (173, FIG. 9A) or in the internal regulator 26-28, FIG. 26.

In a different embodiment, each battery pack could have an internaldigitally stored identification code digitally stored in the batterypack and accessible to an external microprocessor system such as 28-10or 32-10 as in the embodiment of e.g. FIG. 23 (via contacts 23-51A),FIG. 25 (via data output 25-51), FIG. 26 (via components 26-36, 26-37,26-20 and 26-23), or FIG. 27 (via D to A component 27-37 or LANinterface 27-39).

Instead of bringing battery temperature up to ambient temperature as insteps 29-15 to 29-19, it would be conceivable to establish ambienttemperature to match battery temperature, and then proceed with a testfor overcharge condition as in steps 29-20 to 29-23. Similarly beforesteps 29-24 to 29-27, where the battery is initially at a lowtemperature, it would be conceivable to control ambient temperature soas to bring battery temperature up to zero degrees celsius or sixdegrees celsius by control of ambient temperature alone, or incombination with a suitable charging current. In this way, a relativelyhigh charge rate according to FIG. 34 would be suitable, e.g., at least0.6 C, and a maximum overcharge rate according to FIG. 33 would quicklybe appropriate for the overcharge cycle of steps 29-28 and 29-29.

The stored charge rate information can take the form of end points suchas 33-1, 33-2; 33-2, 33-3; 33-3, 33-4, FIG,. 33, for successivesubstantial straight segments such as 33-11, 33-12 and 33-13, so thatthe microprocessor could interpolate a precise charge rate multiplierfor any measured battery temperature. Thus, if segment 33-12 had endpoints at -20° C., 0.060 units and at -10° , 0.100, a batterytemperature of -19° might be computed to correspond to 0.064 by linearinterpolation. Of course of course the points given in Tables I and IIcould be similarly interpolated to obtain intervening more preciseovercharge and fast charge values.

with respect to steps 29-7 to 29-12, an internal microprocessor such asin FIG., 5 or FIGS. 9A, 9B may determine battery load current andcommunicate the same to an external microprocessor such as 28-10 asshown in FIGS. 23, 25, 26 or 27, for example, FIG. 28 may represent theassociation of a non-portable battery conditioning station includingcomponents 28-10, 28-17 and 28-20 with a hand-held terminal unitcontaining a quickly removable battery pack 28-25 comprised of anickel-cadmium rechargeable battery 28-15 and a battery temperaturesensor. 28-16 within housing 28-22. The hand-held terminal unit mayprovide load means 28-21, which may comprise a dynamic random accessmemory and other circuitry which is to be continuously energized duringa charging operation.

As in the embodiment of FIG. 30, the hand-held terminal units which areto be associated with components 28-10, 28-17 and 28-20 may includecoupling means such as 30-21, 30-21A, 30-22, 30-23 and 30-24 which areautomatically engaged with cooperating coupling means of the chargingstation when the hand-held unit is bodily inserted into a receptacle ofthe charging station. The coupling means 30-21 and 30-21A in FIG. 30would be represented in FIG. 28 by a line (+BATT) from component 28-20corresponding to line 28-26, and a further line (+CHG) leading to anetwork (representing components 30-28 and 30-29) in turn connected withbattery 28-15 and line 28-11.

An exemplary charging station adaptable for a hand-held unit includingbattery pack 30-27 of FIG. 30 is shown in greater detail in FIG. 27.

Where FIGS. 28-36 are applied to a system as represented in FIG. 27,components 28-10, 28-17 and 28-20 would be part of charger station27-22. Line 28-26 would lead to a charging station contact engageablewith external battery pack contact 27-11. Input line 28-12 would beconnected via a further set of mating contacts with internal batterypack contact 27-61. Input line 28-11 would connect with contact 27-17.Alternatively, charger station 27-22 would have a LAN interfacecorresponding to 27-39 and would receive digital information as tobattery terminal voltage for example via amplifier 27-35A, an A to Dconverter of terminal 27-10A, LAN interface 27-39 and LAN data couplingmeans 27-19, 27-21. The charging station would then charge the batterypacks such as 27-10B of terminals such as 27-10A in accordance with theembodiments of FIGS. 28-36. In place of amplifier 27-37, (representingcomponents 26-36, 26-37), an identifying shunt voltage regulator 30-10would be part of each battery pack 27-10B.

As a further embodiment, the charger station 27-22 could comprise thecomponents of FIG. 32, the line 28-12 being coupled with a battery suchas 27-27 via mating terminals 32-21 and 27-11 and through forward biaseddiode 27-D1, for example. In this embodiment terminal 27-13 would matewith terminal 32-24, and battery pack 27-10B would conform with batterypack 30-27 for example by including a respective identifying shuntregulator 30-10, and e.g., nickel-cadmium batteries with respectivecharacteristics as shown by FIGS. 33 to 36 and Tables I and II.

Summary of operation of FIGS. 28-36

Operation of the specific exemplary embodiment as presented in FIG. 29may be summarized as follows.

As represented by steps 29-2 and 29-3, the presence of a battery pack28-25, FIG. 28, or 30-27, FIG. 30, may be sensed by means of the Input28-11, FIG. 28 or FIG. 32, from battery pack temperature sensor 28-16,FIG. 28, or 30-26, FIG. 30. A non-zero voltage input level on line 28-11may signal the presence of a battery pack 28-25 coupled with components28-10 and 28-20. The physical connections may be analogous to those ofFIG. 26, for example, an exemplary arrangement of terminals for abattery pack 30-27 being shown in FIG. 30.

Referring to FIG. 31, the load current may be automatically sensed bymeans of steps 29-7 to 29-11 since battery voltage as measured at 28-12,FIG. 28 or FIG. 32, will not increase until a current Ichg, FIG. 30, inexcess of battery load current Iload is applied to line 28-26, FIG. 28.

Where the battery pack has a given upper temperature limit which must beobserved to avoid detriment to battery life, battery may beautomatically allowed to cool to a suitable temperature (e.g. 40° ) ifit is introduced into the charger at an unacceptably high temperature.This is represented by steps 9-13 and 29-14 which may be automaticallyperformed by microprocessor 28-10 or 32-10 according to batterytemperature (Ptemp) as sensed at input 28-11, FIG. 28 or FIG. 32.

As explained in reference to FIG. 36, in order to detect the batteryovercharge condition, the microprocessor 28-10 or 32-10 automaticallyperforms steps 29-15 to 29-19 to assure that battery temperature asmeasured at input 28-11 is not substantially lower than ambienttemperature as sensed at input 28-13. Once battery temperature is atleast essentially equal to ambient temperature, steps 29-20 to 29-23 areeffective to automatically determine whether the battery is to receive afast charge according to steps 29-24 to 29-27, and e.g. FIG. 34, orwhether the microprocessor 28-10 or 32-10 is to govern the supply ofcharging current at 28-26 according to steps 29-28 and 29-29 and e.g.FIG. 33.

Discussion of Terminology

From the foregoing, it will be understood that steps 29-20 to 29-23 areeffective where the battery system can be made to exhibit a temperaturecharacteristic which rises as a function of overcharge current over agiven time interval generally as illustrated in FIG. 32. To accomplishthis the charging system may operate automatically as in steps 29-15 to29-19 to insure that the battery means has a state such that itstemperature will not increase at a substantial rate due to a higherambient temperature (e.g. as in FIG. 36). In particular, the state ofthe battery means may be automatically assured to be such that it willexhibit a substantially greater increase in battery temperature inresponse to a given selected charge rate when the battery is inovercharge condition that when it is not in such a overcharge condition.

As represented by step 29-20, the current automatically applied to thebattery means exceeds battery load current by a substantial overchargemagnitude, e.g. twice the overcharge value obtained from FIG. 33, butthe application is of limited duration (e.g. ten minutes per step 29-20)such as to void substantial detriment to the useful life of the battery.

According to steps 29-22 and 29-23, the microprocessor systemautomatically determines whether any increase in battery temperature dueto step 29-20 is of a magnitude (e.g. two degrees celsius or greater)which is distinctive of the overcharge condition of the battery means.

From the foregoing TABLE I, it will be understood if battery temperatureat step 29-22 has reached thirty degrees celsius, step 29-24 wouldresult in an initial relatively high battery charging current (Ibatt,FIG. 31) of about 1280 milliamperes if the temperature increases at step29-23 was not greater than two degrees celsius, while if the increase atstep 29-23 were found to be greater than two degrees celsius, step 29-28would result in supply of a relatively lower battery charging current ofabout 240 milliamperes.

Where the relatively high battery charging current is applied, batterytemperature is measured at regular intervals (e.g. at about one minuteintervals per step 29-25) to assure that such high charge rate isterminated sufficiently quickly after overcharge condition is detectedso as to avoid any substantial detriment to the useful life of thebattery means.

The overcharge relatively lower charge rate is terminated after anovercharge interval so as to insure optimum charging of the batterymeans without detriment to its useful life.

Of course the charge rate or overcharge rate may be readjusted higher orlower according to FIGS. 33 and 34 at any desired time intervals, e.g.at each step 29-24 in charging mode, and by inserting steps such as29-25 and 29-26 between steps 29-28 and 29-29 so that overcharge currentwould be re-selected at suitable intervals such as one-minute intervals.

Referring to the plots of maximum acceptable overcharge rate in FIGS. 6and 33, it will be observed that there is a minimum temperature for eachbattery type below which overcharge current is not applied by themicroprocessor system 28-10 or 32-10. In FIG. 6, the lower temperatureextreme is shown as about zero degrees Fahrenheit (about minus eighteendegrees celsius). At about zero degrees Fahrenheit, the low overchargerate is less than about capacity divided by fifty. In FIG. 33, the lowtemperature extreme is about minus thirty degrees celsius where theovercharge current of about 0.04 units corresponds to an overcharge rateof about capacity divided by twenty-five.

Above the lower limit temperature, there is a range of temperatureswhere the upper overcharge rate exceeds the lower overcharge rate by afactor of at least about four. For example, in FIG. 6, the acceptableovercharge rate at a relatively high temperature of about one hundredand ten degrees Fahrenheit is close to capacity divided by five (0.2 C),while the acceptable overcharge rate at the low temperature extreme ofabout zero degrees Fahrenheit is about capacity divided by fifty (0.02C)a ratio of overcharge rates of ten to one. According to FIG. 33, themicroprocessor system 28-10 or 32-10 may supply values of overcharge atabout five degrees celsius of about 0.30 units (C/3.3) while at a lowtemperature extreme of about minus thirty degrees celsius, theacceptable overcharge rate to be supplied by the microprocessor systemis about 0.04 units (C/25), a ratio of about seven to one. Between thetemperature values of the temperature range of FIG. 6, the permissibleovercharge rate progressively increases with successively highertemperature values such as zero degrees, fifteen degrees, thirty-fivedegrees, fifty-five degrees, seventy-five degrees and ninety-fivedegrees (Fahrenheit). Similarly in FIG. 33, between temperatures ofminus thirty degrees celsius and about five degrees celsius, thepermissible overcharge rate progressively increases for successivelyincreasing temperature values (such as -20° C., -10° C., and 0° C.).

Referring to FIGS. 28, 30 and 31, it will be understood that theembodiments of FIGS. 28 to 36 avoid series resistance means ofsubstantial ohmic value such as shown at 131, FIG. 9A, 18-26, FIG. 18,24-30, FIG. 24, 25-26, FIG. 25, for sensing battery current. Insteadcharging current source 28-20, FIG. 28, may be automatically operated tosupply desired current values in an open loop manner. An automaticsequence such as steps 29-7 to 29-11 may be used to measure load currentif this would be a fluctuating and possibly significant amount for agiven hand-held terminal unit and would not be reported to the chargingstation by the hand-held unit. As shown by FIGS. 28, 30 and 31, thebattery 28-15 has external terminals e.g. as at 30-21A, 30-22A, FIG. 30,with external circuit means connecting such terminals with the battery,such external circuit means having essentially negligible ohmicresistance such that the battery means supplies load current to a loadvia the external terminals with minimized ohmic loss at the battery sideof said external terminals.

Description of FIGS. 37, 38 and 39

As portable hand-held data and radio terminals continue to be used morewidely in certain demanding applications, the need for fast charging ofthe terminal batteries becomes more significant. The increased use ofhigh powered scanner attachments and peripherals as well as otherconnected devices often causes the terminal battery capacity to be taxedto the point where only a portion of the intended period of usage may beserved with the stored charge available from a single battery pack.Consequently, it has become increasingly necessary to provide multiplepacks which may be exchanged in such a way that a depleted pack may bereplaced by a fresh one with minimal downtime. When a depleted pack isremoved, it should be fully recharged in a least the amount of time thata fresh pack is able to operate the terminal. With a rechargingcapability of this type, it is then possible for virtually perpetualoperation to be provided with as few as two battery packs per terminal.

A similar but further complicated application involves the utilizationof the described data terminals on a vehicle such as an industrial forklift truck. In this type of application, the terminal may receive powerfor operation from the vehicle the majority of the time. Often, however,it may be necessary for the terminal to be physically removed from thevehicle and operated in a fully portable mode for potentially extendedperiods of time. For this reason, it is imperative that the terminalbatteries be maintained in their fully charged or "topped off" state atall times.

The above stated objectives for a battery charging system havetraditionally been extremely difficult to achieve. FIGS. 37, 38 and 39show an embodiment that addresses both aspects of fast charging andmaintenance in a novel and unique way.

As described with reference to FIGS. 28 through 36, the characteristicsof the popular NiCad battery technology are such that the rates at whichcharging may be accomplished are a strong function of temperature andstate of charge. If the cell is in a discharged condition, the rate atwhich charge may be applied is relatively high, regardless of the celltemperature. If the cell is in a charged condition, the rate at whichcharge may be applied to the cell is determined by the temperature ofthe cell. At the limits of cell temperature, excessive charge currentmay cause permanent damage resulting in premature failure of the cell.Consequently, for fast charging to be accomplished safely, thetemperature and state of charge of a battery must be determined.

Battery temperature (herein designated PT) may be measured directly bythe use of a pack temperature sensor 28-16 thermally coupled to thebattery pack 28-25. State of charge of a NiCad battery type is moredifficult to determine. In general, the most reliable indication that aNiCad battery is fully charged is the release of heat while undercharge. This only occurs when the battery is in the overcharge conditionin which most or all of the current supplied to the battery causesevolution of oxygen gas at the positive electrode. When oxygenchemically recombines with cadmium at the negative electrode, heat isreleased. No other condition of operation of a NiCad battery causesappreciable heat to be generated.

In general, the process of converting charge current to stored charge ina NiCad battery is a slightly endothermic chemical reaction, that is,heat is removed from the environment of the battery and it gets slightlycooler. Consequently, it is possible to apply quite high rates of chargeto the battery if it is not in the overcharge condition. Once theovercharge condition is reached, the slightly endothermic chargereaction is overwhelmed by the highly exothermic overcharge/oxygenrecombination reaction. The rate of applied charge must then be quicklyreduced to prevent excessive heating and battery damage

As described in reference to FIGS. 28-36, a microcomputer 28-10 with theability to measure the temperature of a battery and control the appliedcharge to that battery may be employed to effect charging at the maximumsafe (non-damaging) rate and may also terminate the charge function toprevent damage to the battery when it is fully charged. The presentembodiment also employs a microcomputer to measure battery temperatureand control applied charge as indicated in FIG. 28, however, the processthat is used to determine the appropriate charge current is quitesubstantially different, and significantly modifies and improves theperformance of the charging system.

A flowchart of the procedure that accomplishes the described chargingcharacteristics is shown in FIG. 37. It should be noted that thecharging method described may be applied to either a terminal orutilization device with the circuits as shown in FIG. 28 or to astandalone pack charger with one or more sets of the same circuit. Inthe case of the pack charger configuration, the block 28-21 labeled"load" would not be present. In the terminal configuration the operatingpower required by the terminal itself would represent a load thatrequires current to be delivered by the charge circuit or battery.

In FIG. 37, the initial decision block 37-1, |AT-PT|>10° C., providestwo pieces of information based on the ambient temperature value, AT,from sensor 28-17, and battery pack temperature PT. The firstinformation (when the temperature difference is not greater than tendegrees celsius) is that the temperature sensors 28-16 and 28-17 are inat least approximately agreement which provides confidence that they arefunctioning properly. If the temperature difference is relatively great,it is possible that the battery pack and the charger are atsignificantly different temperatures, in which case they need tostabilize to an acceptable level before further procedure steps may betaken. If this condition is detected, a constant current of sixtymilliamperes (60 ma.) is selected as indicated at 37-2 to provide a safelow maintenance current that may minimize further discharge of thebattery if it is already in a relatively depleted state.

If the initial temperature difference is not excessive, the absolutetemperature of the battery pack is examined at steps 37-3 and 37-4. Thetemperature range allowed for charging is between 10° C. and 36° C. Ifthe battery temperature is not within this range, the battery must beallowed to cool or warm as the case may be for the charging process tocontinue. It may be assumed (or specified) that the ambient temperatureenvironment of the charger itself is between these limits, so that thebattery temperature will stabilize after some time to an acceptablelevel. During this temperature stabilization time, it is preferable thatno charge current be supplied to the battery, though it may be necessaryfor current to be supplied to a load, as in the case of a terminal whichreceives it operating power from the battery or charge while charging isin progress. Since the load current is generally not known, a mechanismmust be provided to adjust the current provided by the charger toaccurately match the load current of the terminal. The means by whichthis is accomplished is as follows:

1. Examine the battery pack terminal voltage designated PV as indicatedat block 37-5.

2. Select an initial charge current of sixty milliamperes (60 ma.) asindicated at 37-6.

3. Examine the pack temperature PT at 37-7 and 37-8 to determine if ithas stabilized within the desired limits. If so, return to the maincharging process.

4. Examine the present terminal voltage PV at 37-9 and 37-10.

5. If the battery terminal voltage has increased, decrease the chargecurrent by twenty milliamperes (20 ma.) as indicated at 37-11.

6. If the battery terminal voltage has decreased, increase the chargecurrent by twenty milliamperes (20 ma.) as indicated at 37-12.

7. If no terminal voltage change is detected, leave the charge currentunchanged and return to step 3 above.

This method serves to provide an adaptive current that will prevent thebattery from being further depleted while its temperature stabilizes toan allowable level.

After the battery temperature has stabilized to an allowable level, itis then possible to begin charging at high rates of charge. As describedwith reference to FIGS. 28-36, a stored table containing values ofcurrents that may be safely applied to a battery of a known capacity ata given temperature is used to determine the charge current, this beingindicated at 37-13. While the table values for fast charge current willnot cause stress or damage to a battery when it is discharged andefficiently receiving charge, in general, these charge currents are highenough to cause permanent damage to the battery if not terminatedproperly. The indication that the battery is nearing full charge isbased on detection of the overcharge condition, which is the onlycondition of a NiCad cell that releases significant heat. In flowchartblock of FIG. 37, the condition for decision block 37-14, PT<AT+10° C.,provides the test for overcharge detection. In essence, the test forovercharge is to detect that the battery is becoming warmer than theambient environment, in this case by an amount of ten degrees celsius(10° C.). When this amount of heating is detected indicating that thebattery has reached the overcharge condition in an appreciable amount,the fast charge function is terminated.

Upon completion of fast charge, a maintenance charge function isinitiated which continues to monitor the battery temperature rise abovethe ambient environment (steps 37-15) and maintains an appliedovercharge current at a level that regulates that battery temperaturerise. The overcharge temperature rise is held to eight degrees celsius(8° C.) as shown by steps 37-16, 37-17, and 37-18; this being a safesustainable level that may be maintained indefinitely withoutappreciable cumulative damage to the battery. The temperature regulationprocess is implemented by selecting between a low charge current ofsixty milliamperes (60 ma.) and the higher overcharge current tablevalue depending on the measured temperature rise. By maintaining thebattery n a state of continuous safe overcharge, it is possible to holdthe battery in its maximum state of charge at all times, therebyensuring that the user has the full battery capacity available wheneverneeded. If the battery temperature falls below the ambient temperatureas determined at step 37-15, the fast charge state will be re-enteredwhich will apply the maximum safe charge current for the measuredtemperature. It should be noted that this situation might occur if avery warm battery pack is placed in a pack charger at nominaltemperature. Initially if the temperature difference is greater than 10°C. the pack will be charged at a fixed current of 60 ma until thetemperature difference is reduced. If the pack temperature is less than36° C. at this time, its temperature difference may still be very closeto 10° C. which might allow the process to advance to the finalmaintenance state of the charge system. As the pack cools further due toambient cooling and the endothermic charging reaction, its temperaturemay go below the ambient temperature (step 37-15), it which point thefast charge state would be reentered.

In the maintenance mode, the current required for operation of aterminal is provided by the fact that the charge current (step 37-17 or37-18) will exceed the terminal operating current by an amount necessaryto maintain the temperature rise of the battery. Consequently, thischarging system provides broad flexibility for fast charging of NiCadbatteries in utilization devices with widely varying current demands.

A useful feature of this charging method is that it is not critical thatthe charging voltage source be able to provide the maximum currentspecified by the controlling microcomputer, for reliable charging to beaccomplished. For example, if the selected value of charge current for acertain battery pack is 1500 ma., but the voltage source has a currentcapacity of only 600 ma., the fast charge state of the procedure wouldbe maintained in exactly the same way except it would takecorrespondingly longer for the overcharge state to be reached. Thisfeature of the charging method is particularly useful in configurationswhere multiple battery packs may be charged in a single unit and it isnecessary to place constraints on the unit power supply for economic orsize reasons. It is a relatively simple matter to externally limit themaximum delivered current so that the actual charge current is less thanthe value selected by the controlling microcomputer.

FIG. 38 shows a schematic diagram of a charge current regulator circuitwhich has the capability of delivering a constant current output to abattery in proportion to an input control voltage. In addition, thiscircuit has a maximum delivered current limit that may be set by aresistor selection in power supply constrained applications.

The CHARGE CONTROL input 38-10 is intended to be driven by a digital toanalog (D/A) converter output of a microcomputer based utilizationdevice such as a data terminal. The CHARGE CONTROL input develops acontrol voltage at pin 3 of differential amplifier 38-U1. The output pin1 of 38-U1 drives 38-Q3 which establishes a current through 38-R8 thatdevelops a voltage at 38-UI, pin 4 equal to the voltage at 38-U1, pin 3.Since the current gain h_(fe) of 38-Q3 is relatively high (about 200)the collector current of 38-Q3 is nearly equal to the emitter current,resulting in an equal current through both 38-R5 and 38-R8. Since theseresistors are of equal magnitude, the input voltage at CHARGE CONTROL38-10 appears across 38-R5 referenced to the +12 volt supply voltage.The amplifier at 38-U1A pins 8, 9 and 10 is a differential configurationoperating in a negative feedback mode. With a voltage developed across38-R5, the voltage at pin 9 of 38-U1A will be decreased, which increasesthe voltage at the output pin 8. This increased voltage drives currentinto 38-Q2 which increases the drive current to 38-Q1 establishing acurrent through current sense resistor 38-R6. When the voltage dropacross 38-R6 equals the voltage across 38-R5, the amplifier output willstabilize, holding the output current constant. With a sense resistorvalue of one ohm at 38-R6, the voltage to current conversion factor isone ampere per volt (1 amp./volt). If the CHARGE CONTROL input is leftunconnected, the 1.25 volt voltage reference 38-CR1 and resistors 38-R2and 38-R4 establish an open circuit voltage of 0.120 volts whichestablishes a "default" output current of 120 ma. This condition may beuseful in cases where a utilization device is either unintelligent orits battery is completely depleted in which case its processor is unableto operate and the battery must be brought up to at least minimalcapacity for the processor to function.

The circuit block consisting of the amplifier at 38-U1B pins 5, 6 and 7is a clamp circuit that limits the maximum voltage that may be appliedto 38-U1, pin 3. By limiting the input voltage, the maximum availablecharge current may then be limited to some selected value dependent onthe selection of 38-R15 and 38-R16. With values of twenty-one kilohmsfor 38-R15 and ten kilohms for 38-R16, a voltage of 0.40 volts isapplied to the clamp circuit input. If the input voltage driven onCHARGE CONTROL is less than 0.40 volts, the output pin 7 of 38-U1Bremains low which biases 38-Q4 off. If the CHARGE CONTROL input voltagereaches or exceeds 0.40 volts, 38-Q4 is turned on sufficiently tomaintain a voltage of exactly 0.40 volts at 38-U1B pin 5 which preventsthe input voltage to the control amplifier from exceeding this voltage.The voltage to current transfer function of the system is shown in FIG.39. It should be noted that the clamp voltage and maximum availablecurrent may be modified by selecting different values for 38-R15 and38-R16 or the voltage reference 38-CR1. A maximum available current of1.25 amps may be implemented by deleting 38-R16 in which case the fullreference voltage appears at the clamp circuit input.

The microprocessor system means 28-10 or 32-10 operates automatically toapply substantially maximum charging current to the battery meansconsistent with avoiding substantial detriment to the useful life of thebattery means e.g. as represented in FIG. 34.

DESCRIPTION OF FIGS. 40-46

FIGS. 40-46 illustrate further optional features of the presentinvention. As previously explained, there is room for improvement in theart regarding flexibility and efficiency of the recharging process. Asillustrated previously in FIG. 31, the conventional way of recharging isto simply supply constant charging current to the battery. If, like inFIG. 31, a varying load is connected in parallel with the battery, thismay affect not only the effectiveness and efficiency of recharging, butmay even cause loss of recharging capabilities; or worse, discharge ofthe battery.

It has been found that one way to provide flexibility for recharging andincrease efficiency of recharging is to pulse the recharging current.The pulse width can be modulated according to one or more controls toadjust the net charging current going to the battery.

In FIG. 40, a circuit is illustrated which feeds back information to thecurrent source regarding the amount of recharging current the battery isreceiving. The current source can therefore alter the nature of thecharging current (for example into a pulse width modulated waveform)which can in turn be varied or manipulated to provide a net charge tothe battery. By referring back to FIG. 31, it can be seen that aconstant current source provides constant current I_(chg) (28-26).I_(chg) is divided into battery current I_(batt), directed to thebattery (28-15), and load current I_(load), supplied to the load 28-21.Total current I_(chg) is equal to the sum of I_(batt) plus I_(load). Ifload current I_(load) exceeds constant current I_(chg), current is drawnfrom the battery 28-15.

FIG. 40 shows current source 40-10, load 40-12, and battery 40-14similar to FIG. 31. Additionally, however, a sensor device 40-16 isconnected in series to battery 40-14 to sense the amount of chargingcurrent I_(C) that is given to battery 40-14 by the current I_(B).Sensor 40-16 in turn provides a signal to integrator 40-18 which in turncommunicates with current source 40-10. The signal from integrator 40-18tells charging current source 40-10 the amount of current I_(B) receivedby battery 40-14 over a given period of time. Charging current source40-10 can include some sort of control to vary charging current I_(C) toinsure effective battery recharging even in light of a varying loadwhich draws the varying load current I_(L).

The configuration of FIG. 40 therefore will allow flexible, efficientcontrol of charging current I_(C) to in turn allow flexible andefficient charging of battery 40-14. The pulsing of the current providesa net charge over time to the battery. The magnitude of the net chargecan be adjusted or fine-tuned by varying the pulse width or duty cycleof the pulses.

FIG. 41 shows a slightly different configuration from FIG. 40. Dashedline 41-10 indicates schematically the wall of an enclosed housingcontaining the components of a device including battery 41-12. In thisconfiguration, a controlled switch designated by reference number 41-14pulses the charging current I_(C) to battery 41-12 (current I_(B)) andto other parts of the circuit (current I_(L) for current load). Theadvantages of a pulsed charging current have been previously mentioned.

In FIG. 41 an additional feature is the placement of the source ofcharging current 41-16 externally of the housing of the device. Chargingcurrent source 41-16 would be connectable to the circuitry inside thehousing by a plug-in 41-18 or other suitable connection existing on wall41-10 of the device. FIG. 41 also illustrates an electrical power source41-20 which sends electrical power to charging current source 41-16.Charging current I_(C) would basically be a DC value of constantmagnitude. Control switch 41-14 would then produce a pulsed output. Byplacing the source of charging current 41-16 outside of the housingdevice, any heat dissipated from such a component would be removed frompresenting any problems to the circuitry inside the housing. Thisembodiment therefore provides the advantages of controlling the natureof the form of the charging current to the battery and load, as well asmoving a heat dissipating component outside of the housing. This wouldfurther allow the current source 41-16 to produce a higher level ofcharging current I_(C) then would be possible if source 41-16 werepositioned inside tho housing. This current could then be controlled byswitch 41-14 to provide an adequate net charge to the battery withoutsubstantial danger of the varying load affecting sufficient chargingcurrent to the battery.

FIG. 42 illustrates the basic configuration of FIG. 41, with a specificfeedback circuit and specific controlled switch. In this embodiment,constant current I_(C) is pulse-width modulated by transistor 42-10.Transistor 42-10 is a low on-resistance, high power field effecttransistor providing very low power dissipation. Blocking diode 42-20prevents current flow from battery 42-30 through transistor 42-10. I_(C)divided between battery 42-30 and load 42-80. Sensing resistor 42-40 isa low resistance device which produces a voltage corresponding to thecurrent flow through the battery 42-30. Voltage from sensing resistor42-40 is conditioned by amplifier 42-50. The output voltage of amplifier42-50 is presented to the input of integrator 42-60. Integrator 42-60integrates the voltage input presented to it, thereby integrating thecharge which has flowed into the battery 42-30. The output voltage ofintegrator 42-60, corresponding to the net charge in a given integrationtime interval delivered to the battery 42-30, is presented to pulsewidth modulator 42-70. As the output voltage of integrator 42-60increases, corresponding to increased net charge delivered to thebattery 43-30 per given integration time interval, the width of theoutput pulse of pulse-width modulator narrows. As the duty cycle ofpulse width modulator 42-70 decreases, transistor 42-10 reduces theaverage value of current delivered to battery 42-30 and load 42-80.

FIG. 43 depicts the type of generally square wave, pulse modulatedcharging current I_(C) that is possible with circuits such as shown inany of FIGS. 40-42. In particular, the circuit of FIG. 42 could producethis sort of signal which would have a maximum magnitude well above thatneeded to effectively net charge the battery. However, by pulse widthmodulating I_(C) the net charge can be dynamically controlled to providejust enough charging current I_(B) in addition to accommodating avarying load; due to varying conditions throughout the whole circuit.The circuit of FIG. 42 also has the added benefit of taking the currentsource outside the housing wall to eliminate any heat dissipationproblems.

FIG. 44 illustrates a still further alternative for the invention.Similar to FIGS. 41 and 42, electrical power source 44-10 and constantcurrent source 44-12 are located outside of the housing wall 44-14 forthe device. The major difference between the configuration of FIG. 44and that of FIG. 42 is that it can produce a generally trapezoidalshaped pulse such as is shown in FIG. 45, instead of generallyrectangular or square wave pulse of FIG. 43. The benefit of such apulse-shape is to reduce both conducted and emitted transients deliveredto the load circuits.

FIG. 44 shows the use of a "miller integrator" with a transistor switch(see dashed line 44-16) to produce the trapezoidal shape. In thisconfiguration, the miller integrator receives the signal from the pulsewidth modulator (see FIG. 42) and produces the trapezoidal shape pulsewidth modulated current signal illustrated in FIG. 45. FIG. 46 shows thevoltage rendition of the pulse width modulated current wave of FIG. 45.

It will be apparent that features of the various embodiments describedor incorporated herein may be combined, and that various of the featuresmay be utilized independently of others, and that many furthermodifications and variations may be effected without departing from thescope of the teachings and concepts of the present disclosure.

I claim as my invention:
 1. An apparatus for providing charging currentto a rechargeable battery associated with a device which presents avarying load to the battery during recharging comprising:connectionmeans for electrically coupling a battery to a source of chargingcurrent, where the battery is connected to the device which presents avarying load and the charging current generally has a fixed DCamplitude; pass means operatively positioned between the connectionmeans and the battery for selectively passing the charging current tothe battery to modify the charging current into a pulsed wave form, saidpulsed wave form having a plurality of pulses with pulse widths whichare dependent on a desired level of net charging current; and so thatpulsed current provides the desired level of net charging current to thebattery over time while the battery is connected to the device whichpresents a varying load.
 2. A method for providing charging current to abattery associated with a device presenting a varying load to thebattery during charging comprising:providing a regulated generally fixedamplitude charging current from a charging current source to thebattery; and pulsing the charging current through the battery so thatthe battery receives a net charging current over successive periods oftime while the battery is connected to the device presenting a varyingload to the battery, wherein duration of individual charging currentpulses of the pulsed charging current depends on a desired net chargingcurrent.
 3. The apparatus of claim 1 wherein said charging current is apulse width modulated signal.
 4. The apparatus of claim 1 wherein saidpass means is comprised of a switching device which is controlled by amodulated signal.
 5. The apparatus of claim 1 wherein the desired netlevel of charging current is determined by the amount of chargingcurrent that is provided to the battery.
 6. The apparatus of claim 1further comprising a current sensor operatively coupled to the batteryto sense the amount of charging current supplied to the battery, whereinthe pulse widths are dependent upon a sensed charging current.
 7. Themethod of claim 2 further comprising the steps of:sensing the chargingcurrent provided to the battery; and controlling the pulsing of thecharging current depending on the sensed charging current.
 8. The methodof claim 2 wherein the desired level of net charging current depends onthe charging current supplied to the battery.
 9. The method of claim 2further comprising the step of providing a switching device connectedbetween the charging current source and the battery, wherein the pulsedcharging current is pulsed by oscillating the switching device.
 10. Acircuit for providing charging current to a rechargeable batteryassociated with a device which presentsa varying load to the batteryduring recharging comprising: a current source; a current sensoroperatively coupled to the battery for sensing the current through thebattery and producing a control signal in response to the sensedcurrent; and a switching device connected between the current source andthe battery, said switching device being operatively connected to saidcurrent sensor such that the control signal causes the switching deviceto repeatedly turn on and off to provide a pulsed charging current tothe battery.
 11. The circuit of claim 10 wherein said switching devicecomprises a transistor.
 12. The apparatus of claim 10 wherein saidcontrol signal comprises a pulse width modulated signal.
 13. A method ofproviding charging current to a rechargeable battery inside a housing ofa device which presents a varying load to the battery during recharging,comprising the steps of:connecting the device to a source of chargingcurrent located external to the housing of the device; providing acontrol signal; selectively passing the charging current from the sourceof charging current to the battery according to the control signal;monitoring the amount of the charging current received by the batteryand generating the control signal based on the amount of the chargingcurrent received by the battery; and controlling the net amount of thecharging current received by the battery for a given time by causing thecontrol signal to increase and decrease the net amount of chargingcurrent passing through the pass means.
 14. An apparatus for charging abattery contained within a housing of a device, where the battery isconnected to a varying load and charging current for a given time isprovided by a charging current source, said apparatus comprising:aconductor for communicating the charging current from the chargingcurrent source to the battery; a switching device positioned between thecharging current source and the battery for converting the chargingcurrent from the charging current source into a pulsed currentconsisting of successive pulses having a duty cycle and a net value ofcharging current for a given time; a sensor associated with the batteryfor sensing the net value of the charging current at the battery; and acontroller for receiving at the battery the net value of chargingcurrent for a given time, comparing it to a target net value, andadjusting operation of the switching device to vary the duty cycle ofthe pulsed current to maintain the target net value at the batteryregardless of the varying load.
 15. An apparatus for charging a batterycontained within a housing of a device, where the battery is connectedto a varying load and charging current for a given time is provided by acharging current source, said apparatus comprising:a switching devicepositioned between the charging current source and the battery forconverting the charging current from the charging current source into apulsed current consisting of successive pulses having a duty cycle and anet value of charging current for a given time; a sensor associated withthe battery for sensing the net value of the charging current for agiven time at the battery; a controller for receiving the net value ofcharging current at the battery for a given time, comparing it to atarget net value for and adjusting operation of the switching device tovary the duty cycle of the pulsed current to maintain the target netvalue at the battery regardless of the varying load; and said chargingcurrent source comprising a current regulator to produce the chargingcurrent.
 16. An apparatus for charging a battery pack for powering adevice external to the battery pack, where the battery pack is connectedto a varying load and charging current is provided by a charging currentsource external to the battery pack, said battery pack comprising:abattery pack housing; a battery disposed within the battery packhousing; a switching device disposed within the battery pack housing andbeing operatively connected between the charging current source and thebattery; a processor disposed within the battery pack housing and beingelectrically connected to the switching device for providing a controlsignal to the switching device in order to control the net chargingcurrent supplied to the battery; and a sensor operatively connected tothe processor for sensing at least one operating parameter of thebattery, wherein the net charging current supplied to the battery iscontrolled based on the sensed operating parameter of the battery. 17.An apparatus for charging a battery contained within a housing of anelectronic device, where the battery is connected to a varying load andcharging current is provided by a charging current source external tothe housing of the electronic device, said apparatus comprising:aswitching device disposed within the housing of the electronic deviceand being operatively connected between the external charging currentsource and the battery; a processor disposed within the housing of theelectronic device and being electrically connected to the switchingdevice for providing a control signal to the switching device in orderto control the net charging current supplied to the battery; and asensor operatively connected to the processor for sensing at least oneoperating parameter of the battery, wherein the net charging currentsupplied to the battery is controlled based on the sensed operatingparameter of the battery.
 18. An apparatus for charging a batterycontained within a housing of a device, where the battery is connectedto a varying load and charging current for a given time is provided by acharging current source, said apparatus comprising:a switching devicepositioned between the charging current source and the battery forconverting the charging current from the charging current source into aconverted charging current having a net value of charging current for agiven time; a sensing component operatively connected to the battery toreceive current corresponding to the net value of the charging currentreceived by the battery; an amplifier connected to the sensing componentfor producing an amplified signal correlated to the net value ofcharging current to the battery; and a controller for receiving theamplified signal and adjusting operation of the switching device tomaintain a target net charging current at the battery regardless of thevarying load.